Clutches are devices used to selectively connect a source of rotational power to a driven mechanism. For instance, in a vehicle drive-train system, a clutch is used to drivingly connect an engine to a transmission. When the engine is drivingly connected with the transmission by the clutch, vibrations are transmitted between the clutch and the transmission and other drive-train components, producing undesirable operating conditions, such as gear rattle or ‘growl’, which may produce an undesirable amount of noise and/or transmit vibrations through vehicle components to a user.
Centrifugally operated friction clutches typically include an input member driven by a prime mover, usually an electric motor or internal combustion engine. Further, such clutches also include weights rotatable with the input member which, upon rotation of the driving member, will move radially outwardly under the effect of centrifugal force to cause the input member to frictionally engage a driven output member.
Automatically actuated centrifugal clutches employed with heavy-duty electromechanical highway line-haul truck transmissions may include centrifugal actuation modules that house the centrifugally actuated weights. The centrifugal actuation modules are drivingly connected to an engine flywheel, and each of a plurality of centrifugally actuated weights may be adapted to swing in an arc about a pivot link fixed to a module housing structure. As such, the swing weights contained within the modules are radially outwardly movable against resistive spring forces as a function of engine speed—the higher the speed, the greater the outward movement between limits. Rollers attached to the weights selectively roll atop ramp segments that are cammed for clutch engagement and disengagement.
The driven output member typically includes a clutch hub engaged for rotation with a transmission input shaft and a clutch disk selectively engaged for rotation with the engine flywheel and a portion of the input member. To reduce the transmission of vibrations, the driven member typically employs a plurality of compression damping springs between the clutch hub and the clutch disc. These springs are typically disposed in spring pockets circumferentially located around the clutch hub. Compression of the damping springs is limited by stops disposed between the hub and the clutch disk, limiting the deflection of the damping springs and the relative rotation therebetween the hub and the clutch disk. Each of the damping springs may have a similar spring modulus and limit of deflection, or the springs may be grouped into multiple stages to provide differing levels of damping at differing values of transmitted torque. The damping springs provide some degree of isolation between the engine and transmission to reduce the transmission of vibration due to engine firing pulses and other engine speed fluctuations. However, vibrations can still be transmitted through the damping springs to produce gear rattle.
During clutch engagement and operation, excessive torsional excitation can generate noise even with damping springs incorporated into the driven member. It is believed that the damping springs contribute to this noise by allowing the teeth of the meshing gears within the transmission to impact on both the ‘drive side’ and the ‘coast side’ of the teeth. This ‘double impacting’ is thought to be caused as the torque applied through the driven member is within a range of values that permits a transmission of torque through the drive sides of the teeth, which deflects the damping springs almost instantaneously to eliminate the contact between the drive sides of the teeth as the ‘driven gear’ rotates momentarily at a greater speed than the ‘driving gear’. When the contact between the drive sides of the teeth is eliminated, the coast sides of the teeth may impact, causing the driving gear to momentarily increase in speed such that the drive sides of the teeth then impact. In an undesirable operational state, the double impacting may be self propagating until factors such as torque applied, vehicle speed, or gear engagement, are changed.
When operating a drive train system without a centrifugal clutch, the operator may engage or disengage the clutch slightly to bring the drive train system out of an undesirable double impacting condition. In a drive train system with a centrifugally operated master clutch, the clutch engagement is typically controlled by engine speed, and an operator may not have a convenient opportunity to manually control the drive train system out of an undesirable condition, such as the double impacting condition or other conditions.
One solution to further reducing some of the transmission of vibrations has been to split the hub into an inner hub directly connected to the transmission input shaft and a coaxial outer hub connected to the clutch disc through the damping springs. The inner hub and outer hub may be configured to provide a predetermined amount of rotative lash therebetween. A predamper is placed between the inner hub and the outer hub. The predamper has springs selected to further damp out vibrations that can induce gear rattle or other undesirable operational conditions. Typically, the predamper will absorb about 10 ft·lb (13.5 N·m) before the compression of the predamper springs is limited by predamper stops.
However, the predamper is insufficient to reduce all undesirable noise and vibrations within the transmission during operation, especially during operational events that involve a high torque load. What is needed, therefore, is a method and/or apparatus to reduce noise and vibrations within a drive train system during predictable operational conditions.